1. Field of the Invention
The invention relates to a secondary burner for a gas turbine combustion chamber, for example, in which a fuel feed arranged in a combustion chamber wall is surrounded by an annular air duct.
2. Discussion of Background
Secondary burners in gas turbine combustion chambers are used with advantage where very low-emission combustion of oil or gas is the objective. The gas flow downstream of the normal burner, into which fuel has already been introduced from a primary source, can have an average temperature of approximately 850.degree. C. in this case. In such an environment, fuel which is sprayed in by means of a secondary burner can be ignited sufficiently rapidly. The ignition delay period is so short that the secondary combustion process is initiated over a useful distance, for example between 2 and 10 cm.
In contrast to normal burners, however, secondary burners are not self-sustaining. A flame stabilization zone is deliberately avoided in this case. A secondary burner therefore offers the possibility of converting a very large amount of fuel even at very high velocities, i.e. in very small periods of time. Its advantage lies in the fact that the residence time in a zone which is not perfectly premixed can be kept almost arbitrarily short. It is therefore, possible to mix very rapidly at high velocity.
For this purpose, the fuel or an air/fuel mixture from the secondary burner is, as a rule, blown with a transverse jet into the secondary combustion space, where rapid and homogeneous mixing takes place. This is not possible in the case of conventional burners because the flame stabilization necessary there would be lost.
The dominant problem in a secondary burner is that it is very susceptible to vibration. This is due to the fact that there is no unambiguously defined reaction zone, such as exists in the case of a normal burner. Because reaction zones can be easily influenced by pressure perturbations, such pressure perturbations can lead to large-volume displacements of the reaction in the combustion space and this can lead to very strong vibrations.